Molybdenum is a tough, ductile metal that is characterized by moderate hardness, high thermal and electrical conductivity, high resistance to corrosion, low thermal expansion, and low specific heat. Molybdenum also has a high melting point (2610° C.) that is surpassed only by tungsten and tantalum. Molybdenum is used in a wide variety of fields, ranging from aerospace, to nuclear energy, to photovoltaic cell and semiconductor manufacture, just to name a few. Molybdenum is also commonly used as an alloying agent in various types of stainless steels, tool steels, and high-temperature superalloys. In addition, molybdenum is often used as a catalyst (e.g., in petroleum refining), among other applications.
Molybdenum is primarily found in the form of molybdenite ore which contains molybdenum sulfide, (MoS2) and in wulfenite, (PbMoO3). Molybdenum ore may be processed by roasting it to form molybdic oxide (MoO3). Molybdic oxide may be directly combined with other metals, such as steel and iron, to form alloys thereof, although ferromolybdenum (FeMo) also may be used for this purpose. Alternatively, molybdic oxide may be further processed to form molybdenum metal (Mo).
Processes for producing molybdenum metal may be broadly categorized as either two-step reduction processes or single stage reduction processes. In both types of processes, the molybdenum metal is typically recovered in powder form. The starting material may be either oxide or molybdate, the choice being determined by a variety of factors. The most widely used starting material is chemical grade trioxide (MoO3), although the dioxide (MoO2), and ammonium dimolybdate ((NH4)2Mo2O7), are also used.
While molybdenum metal powders produced by such single-and two-stage processes may be subsequently melted (e.g., by arc-melting) to produce molybdenum metal ingots, the high melting temperature of molybdenum as well as other difficulties with arc-melting processes make such processing undesirable in most instances. Instead, molybdenum metal powders are usually subjected to a number of so-called “powder metallurgy” processes to form or produce various types of molybdenum metal articles and materials. For example, molybdenum metal powder may be compacted into bars or “compacts,” that are subsequently sintered. The sintered compacts may be used “as is,” or may be further processed, e.g., by swaging, forging, rolling, or drawing, to form a wide variety of molybdenum metal articles, such as wire and sheet products.